Injection laser modulator

Abstract

A carrier-injected avalanche device series connected to a forwardly-poled injection laser generates a current pulse, which may be as short as one nanosecond, through the injection laser only when both a direct current bias voltage is applied across this series connection from a charge supply and carriers have been injected into the device in response to the leading edge of a modulation trigger pulse. This current pulse through the injection laser is of sufficient magnitude to effect pumping thereof, so that the injection laser emits a corresponding pulse of coherent light, which may also be as short as one nanosecond.

What is claimed is: 
     
       1. In combination, a carrier injected avalanche device, an injection laser connected in series with said avalanche device for generating a pulse of coherent light from said injection laser only when both a direct-current voltage of given magnitude across said avalanche device is applied thereto through said injection laser with said injection laser poled to be forwardly conducting and at least a given amount of carriers are injected into said avalanche device, a charge supply circuit coupled across said serially-connected avalanche device and injection laser for supplying said direct-current voltage across said avalanche device until avalanching in said avalanche device has taken place, and modulation signal means for injecting said carriers into said avalanche device. 
     
     
       2. The combination defined in claim 1, wherein said modulation signal means comprises a pulse code modulator whereby said injection laser transmits coherent-light pulses corresponding to the pulse code from said modulator. 
     
     
       3. The combination defined in claim 1, wherein said charge supply circuit comprises a charge storage device and a charging circuit for charging said charge storage device to a potential substantially equal to said direct-current voltage. 
     
     
       4. The combination defined in claim 3, wherein said charge storage device comprises a capacitance and said charging circuit comprises a resistance coupling said charge storage device to a point of fixed potential. 
     
     
       5. The combination defined in claim 1, further including a light-pumped crystal laser which continues to lase for at least a given time interval after the termination of light-pumping thereof, said crystal laser being positioned to be illuminated and light pumped by coherent light pulses from said injection laser and wherein said modulation signal means comprises means for applying a series of carrier-injection pulses to said avalanche device at a pulse repetition period equal in duration to said given time interval, whereby said crystal laser operates as a CW laser. 
     
     
       6. The combination defined in claim 5, wherein said crystal laser is a YAG laser.